This invention relates to a center assembly including an oil reservoir for machine tools.
The term "machine tool" as used herein and in the appended claims includes all machine tools, such as lathes and cylindrical grinders, which are equipped with a tailstock.
When work is machined on a machine tool, the work is supported by a chuck at one end and by a center at the other end, with the front end of the center fitted in a center hole in the work. The work thus supported is driven. Accordingly, friction occurs between the front end of the center and the inner surface defining the center hole of the work, possibly causing damage to the tip of the center with the resulting heat. For this reason, it is impossible to rotate the work at a high speed when the work is supported by a usual dead center. This drawback may be overcome by a center in which the front end alone is made of cemented carbide alloy or by a so-called live center comprising a body portion and a front end portion mounted on the body portion by a bearing and rotatable with the work. With the former center, however, frication still takes place between the cemented carbide front end and the inner surface defining the center hole of the work, consequently limiting the speed of rotation of the work. Although the latter involves no friction between the front end portion and the work and is therefore free of the damage to be otherwise caused by frictional heat because the front end portion is rotatable with the work, the rotatable front end portion tends to deflect due to the high-speed rotation of the work, reducing the dimensional accuracy of the work obtained. Furthermore, the center is complex to make.